Abstract：
Na3V2(PO4)2F3 (NVPF), a typical sodium superionic conductor (NASICON) type structure, has attracted much interest as a potential positive electrode in sodium-ion battery. However, the inherently poor electronic conductivity of phosphates compromises the electrochemical properties of this material. Here, we develop a general strategy to improve the electrochemical performance by preparing a new composite material \"polyaniline (PANI)@NVPF\" using a Pickering emulsion method. The X-ray diffraction and Raman results indicated a successful PANI coating without affecting the NASICON-type structure of NVPF, and they enhanced the interfacial bonding between the two components. Also, thermogravimetric analysis and scanning electron microscopy analyses revealed that the PANI content influenced the thermal stability and morphology of the nanocomposites. As a result, the sodium test cells exhibited multielectron reactions and a better rate performance for PANI@NVPF nanocomposites as compared to NVPF. Specifically, 2%PANI@NVPF maintained 70% of its initial capacity at 5C. Ex-situ electron paramagnetic resonance revealed the existence of mixed valence states of vanadium (V4+/V3+) in both discharge and charge processes. Consequently, the successful PANI coating into the sodium superionic conductor framework improved the sodium diffusion channels with a measurable increase of diffusion coefficients with cycling (ca. 3.25 × 10-11 cm2 s-1). Therefore, PANI@NVPF nanocomposites are promising cathode candidates for high-rate sodium-ion battery applications.
摘要：
Na3V2(PO4)2F3(NVPF),典型的钠超离子导体（NASICON）型结构，作为钠离子电池中的潜在正极，引起了人们的极大兴趣。然而,磷酸盐本身较差的电子导电性会损害这种材料的电化学性能。这里,我们通过使用Pickering乳液法制备新型复合材料“聚苯胺（PANI）@NVPF”来制定提高电化学性能的一般策略。X射线衍射和拉曼结果表明，在不影响NVPF的NASICON型结构的情况下，成功的PANI涂层。它们增强了两种组分之间的界面结合。此外，热重分析和扫描电子显微镜分析表明，PANI含量影响纳米复合材料的热稳定性和形态。因此,与NVPF相比，钠测试电池表现出多电子反应和PANI@NVPF纳米复合材料更好的倍率性能。具体来说,2%的PANI@NVPF在5C时保持了其初始容量的70%。非原位电子顺磁共振揭示了在放电和充电过程中均存在钒的混合价态（V4/V3）。因此,成功的PANI涂层到钠超离子导体框架中改善了钠扩散通道，随着循环的扩散系数可测量地增加（约3.25×10-11cm2s-1)。因此,PANI@NVPF纳米复合材料是高倍率钠离子电池应用的有前途的阴极候选物。
